1. Field of the Invention
The present invention relates to a method and an apparatus for optically reading a target, such as information.
2. Description of the Related Art
A conventional handheld optical information reader aims at reading, as a target, information that is optically readable, such as a barcode, a two-dimensional code, or other similar codes. The optical information reader has a handheld body case, a photodetector, an imaging unit with an imaging lens, and a reading unit composed of a lighting device. The photodetector, the imaging unit, and the reading unit are installed in the body case, respectively.
In the optical information reader, light is supplied from the lighting device through a reading window formed at one end portion, that is, a head portion, of the body case. The light is irradiated to a target, such as a barcode. Light reflected from the target based on the irradiated light is entered through the reading window into the imaging unit. The light entered into the imaging unit is focused on the photodetector by the imaging lens to be imaged thereon, so that an image corresponding to the target is picked up by the photodetector.
In the above optical reading structure of the optical information reader, the range of a reading distance defined as a distance between the reading window and a target that is readable by the optical information reader is previously determined depending on an optical characteristic of the imaging unit, such as a focal length of the imaging lens. A user, therefore, handles the body case of the optical information reader to locate it so that the reading window of the body case is positioned at the reading distance from the target or adjacent to the reading distance and the reading window is opposite to the target. After the positioning of the reading window of the body case of the optical information reader, the reading operations of the target set forth above are started.
For expanding the range of a reading distance, an optical information reader having a mechanism capable of sliding the imaging lens to adjust a focal point of the imaging lens has been created in recent years.
An example of the optical information reader with the focal point adjusting mechanism is disclosed in Japanese Unexamined Patent Publication No. H7-319990.
In the disclosed optical information reader, a focal point adjusting mechanism composed of a ball thread mechanism and a stepping motor is provided. The ball thread mechanism and the stepping motor are designed to slide a focal lens linearly along an optical axis of the focal lens to adjust a focal point of the focal lens.
The structure and adjusting operations of the disclosed focal-point adjusting mechanism may be comparatively complicated. Especially, the linearly sliding structure of the focal lens may cause the focal-point adjusting mechanism itself to be complicated and upsized. The slide portion of the focal-point adjusting mechanism, such as the focal lens, may be comparatively heavy, resulting in a delay of the sliding response of the slide portion.